In recent years, the use conditions of vacuum interrupter users have become severe, and the expansion of applying vacuum interrupters to capacitor circuits has been progressing. In capacitor circuits, the voltage that is the double or triple of normal voltage is applied between the electrodes. With this, the contact surface tends to be considerably damaged by arc at the time of the current breaking and the current opening and closing, and reignition of arc tends to occur. Therefore, there is an increasing demand for electrode materials having breaking capabilities and withstand voltage capabilities, superior to those of conventional Cu—Cr electrode materials.
For example, in Patent Publication 1, there is described a method for producing an electrode material, in which, as a Cu—Cr based electrode material excellent in electrical characteristics such as current breaking capability and withstand voltage capability, respective powders of Cu used as a base material, Cr for improving electrical characteristics, and a heat-resistant element (Mo, W, Nb, Ta, V, Zr) for making the Cr particles finer are mixed together, and then the mixed powder is put into a mold, followed by pressure forming and making a sintered body. Specifically, a heat-resistant element, such as Mo, W, Nb, Ta, V or Zr, is added to a Cu—Cr based electrode material containing as a raw material a Cr having a particle size of 200-300 μm, and the Cr is made fine through a fine texture technology, an alloying process of the Cr element and the heat-resistant element is accelerated, the precipitation of fine Cr—X (Cr making a solid solution with the heat-resistant element) particles in the inside of the Cu base material texture is increased, and the Cr particles having a diameter of 20-60 μm in a configuration to have the heat-resistant element in its inside are uniformly dispersed in the Cu base material texture. Furthermore, in Patent Publication 1, there is a description that it is important to increase the content of the Cr or the heat-resistant element in the Cu base material in the Cu based electrode material and to conduct a uniform dispersion after making the particle size of Cr, etc. fine, in order to improve electrical characteristics such as current breaking capability and withstand voltage capability in electrode materials for vacuum interrupters.
Furthermore, in Patent Publication 2, without going through the fine texture technology, a powder obtained by pulverizing a single solid solution that is a reaction product of a heat-resistant element is mixed with a Cu powder, and this mixed powder is subjected to pressure forming and then sintering to produce an electrode material containing Cr and the heat-resistant element in the electrode texture.
Furthermore, in Patent Publication 3, the mixing ratio of Mo powder to Cr powder is made to be Mo:Cr=1:1 to 9:1, Mo is made to be equal to or greater than Cr in mixing weight, and they are uniformly mixed together, thereby producing an electrode material that has a fine texture although it is a MoCr alloy's composite texture high in arc-resistant component content. Such electrode material is capable of improving breaking capability of vacuum interrupters. Furthermore, since it is possible to further increase electrode material's hardness, it is mentioned that vacuum interrupter's withstand voltage and/or capacitor's opening and closing capability can also be improved.